In radio frequency (RF) applications, it is commonplace to split and/or combine signals, and there are a variety of ways in which this can be accomplished. One example is a Wilkinson splitter/combiner 100, which can be seen in FIG. 1. Typically, a Wilkinson splitter (or combiner) 100 is a 2-to-1 splitter (or combiner) having input port WIN and output ports WOUT1 and WOUT2. The distances D2 and D3 along the outer diameter of the splitter 100 is on the order of one-quarter of the wavelength for the frequency-of-interest, and the distance D1 along the inner diameter of the splitter 100 is on the order of one-half the wavelength for the frequency-of-interest. Additionally, an impedance element (i.e., resistor) 102 is coupled between ports WOUT1 and WOUT2 to allow for isolation and proper impedance matching.
In another alternative approach, a hybrid coupler or rat-race 200 (as shown in FIG. 2) can be employed. As shown, this coupler 200 is generally curvilinear (i.e. circular) with an inner diameter (which can, for example, be one and one-half the wavelength of the frequency—of interest). This coupler 200 has an input port RIN and output port ROUT1 and ROUT2 (which are capable of outputting signals outputting signals at approximately one-half the input power). Additionally, there is an isolation port RISO that is terminated with an impedance element (i.e., resistor) 202.
Each of these different approaches can be adequate under appropriate conditions (i.e., <10 GHz); however, for high speed applications (i.e. terahertz or millimeter wave), these approaches may not be adequate. In particular, the physical terminations (i.e., impedance elements 102 and 202) may be prohibitive in terms of both cost and size. Therefore, there is a need for an improved combiner/splitter.
Some examples of conventional systems are: U.S. Pat. Nos. 4,254,386; 4,956,621; 6,674,410; and European Patent No. EP1042843.